This invention relates to polyphenyleneoxide resin compositions having improved resistance to deterioration in mechanical properties upon thermal aging as a result of incorporating new phenyl acid phosphite stabilizers.
Polyphenylene oxide resin compositions also known as polyphenylene ether resin compositions are well known as a class of thermoplastic materials possessing outstanding hydrolytic stability, dimensional stability, and dielectric characteristics over a range of service temperatures extending well above those characteristic of commodity thermoplastics such as the olefin and vinyl chloride polymers. The very properties, however, that make polyphenylene oxide particularly useful also require that the material be fabricated into finished products under severe conditions of processing temperature and shear in the presence of oxygen during the formation of film, fiber, and molded articles. Under these conditions, polyphenylene oxide resin compositions are sensitive to the degradative influence of oxygen and heat and deteriorate in properties unless adequately stabilized.
For example, S. Nakashio in U.S. Pat. No. 3,578,625 of May 11, 1971 has disclosed measurements of the degree of discoloration of a sheet of polyphenylene oxide when pressed for 5 minutes at 270.degree. C.; the amount of oxygen absorbed into a film of 0.01 mm. thickness during 3 hours of heating at 160.degree. C.; and the change in light absorption of such a film during the 160.degree. C. exposure for 3 hours. According to Nakashio, deterioration of polyphenylene oxide as measured in these ways is lessened by the addition of a combination of stabilizers, including at least one kind of hindered phenol and at least one member selected from the group of trialkyl or triaryl thiophosphites, thioethers of carboxylic acid esters, thioethers, and metal alkyl- or metal aryldithiocarbamates.
A Katchman et al in U.S. Pat. No. 3,761,541 of Sept. 25, 1973, after reviewing earlier proposals for improving the resistance of polyphenylene oxide polymer to the degradative effects of oxygen, disclosed a stabilizer combination comprising an alkanolamine alone or in combination with an organic phosphite, an inorganic sulfide, and mixtures thereof. According to Katchman, the phosphites include those of the formula ##STR2## wherein R is independently selected from the group consisting of hydrogen and substituted and unsubstituted hydrocarbon groups containing up to about 20 carbon atoms including saturated and unsaturated, straight, branched chain and mono-cyclic and polycyclic groups. Suitable examples of these compounds are those wherein R is hydrogen, straight or branched chain alkyl of from 1-20 carbon atoms, alkenyl of from 1-20 carbon atoms, (lower)-alkylphenyl, phenyl, halo alkyl of from 1-20 carbon atoms, and substituted phenyl wherein the substituents may include one or more halogen, hydroxy or (lower)alkyl groups. Suitable ex
Specific examples are given at column 4 lines 1 to 34 and include many triphosphites such as triphenyl phosphite, trilauryl phosphite, and 2-ethylhexyl di(p-tolyl phosphite), and such diphosphites (also known as hydrogen phosphites or acid phosphites) as bis(2-ethylhexyl) hydrogen phosphite, allyl phenyl hydrogen phosphite, and diphenyl hydrogen phosphite. J. Bussink in U.S. Pat. No. 3,453,231 of July 1, 1969 disclosed a stabilizer combination of a boron compound such as a boron oxide, boric acid, or a boric acid ester, with a phosphorus compound represented by the formula O.sub.n PXYZ in which n is zero or 1, X is selected from OR, SR, and NR.sub.2 groups where R is a substituted or unsubstituted alkyl group, and Y and Z are selected from OR', SR', and NR'.sub.2 groups where R' is R or hydrogen. S. Yamonouchi in U.S. Pat. No. 3,700,750 of Oct. 24, 1972 disclosed the manufacture of polyphenylene oxide resin compositions by the polymerization of styrene in the presence of a polyphenylene oxide, with or without the presence of a rubber as well. Yamonouchi's compositions are stabilized with a combination of (a) a hinderedphenol, and (b) at least one member of the groups thioether acid esters, trialkyl phosphites, trialkyl thiophosphites, triaryl phosphites, triaryl trithiophosphites, and arylamines, or (c) at least one member of the groups metal dithiocarbamates, metal imidazoline-2-thiolates, and zinc benzothiazole-2-thiolate.
G. McNally in U.S. published patent application B 054,859 of Feb. 17, 1976 has disclosed the stabilization of various polymers including polyphenylene oxides with a combination of an ultraviolet absorber and a thiophosphite of the formula ##STR3## where n is zero or an integer, preferably not over 9, R is a divalent aromatic, aliphatic or cycloaliphatic group, R.sub.1 is alkyl, haloalkyl, aryl, haloaryl, alkenyl, haloalkenyl, cycloalkyl or aralkyl. The R.sub.1 groups can be the same or different.
V. Abolins in U.S. Pat. No. 4,154,719 of May 15, 1979 disclosed a thermoplastic composition comprising a polyphenylene oxide resin, a rubber modified alkenyl aromatic resin, and a hindered tris-phenol having three hindered phenolic groups attached to a triazine ring; tridecyl phosphite is used as an additional stabilizer ingredient in certain Examples.